Boiler efficiency calculation methods are useful for determining which operating methods will reduce the amount of fuel required. Because there are many variations in the combustion process and many control settings available to meet steam demands, some type of efficiency calculation is necessary.
An on-line efficiency calculation is desirable due to the fact that the combustion process is highly variable with constant changes in load demand and gradual, long term changes in burner equipment efficiency and ambient atmospheric conditions.
Fuel heating value can also vary for fuels such as bark, refuse, blast furnace gas, residue oils, waste sludge, or blends of coal. As a result, control settings, based on steady state calculations of boiler efficiency using average daily or weekly fuel/air and fuel heating values, may not result in the most economical operation of the boiler.
For systems with multiple boilers, operating costs may be reduced thru the use of boiler management optimization and load allocation systems. Boiler management systems set the fuel firing to the various boilers to minimize fuel costs. Some reliable measurement of boiler efficiency is required with these systems to obtain maximum fuel savings.
One technique for determining the efficiency of a fossil fuel-fired steam generator, as set forth in the ASME/ANSI Power Test Codes, is the so-called Heat Loss Method which is based on the calculation of heat losses per pound of fuel. The generator efficiency is then the difference between the higher heating value of the fuel minus the total of the calculated heat losses, expressed in percent, for given feedwater conditions.
A complete efficiency test of a fossil fuel-fired steam generator as presently conducted requires many manhours of labor to record the required data at stipulated increments of time over an extended period of time and then to make the necessary calculations at each of several loads. Furthermore, to obtain meaningful results, during the period of time in which the tests are conducted, the generator must be held in a steady-state condition. For these reasons efficiency tests are usually conducted only when required to meet performance guarantees.
Bonne et. al. (GF Pat. No. 2,016,707 A) recites a flue gas loss or combustion efficiency meter primarily for use in furnaces using natural gas. Compensation is not made for losses due to incomplete combustion, radiation, air leaks, blowdown, moisture in the air, and unburned carbon in the ash. The present invention compensates for all of these losses and results in a system capable of measuring the boiler efficiency of a furnace utilizing most fuels including coal, oil, natural gas, hydrogen, etc.
With the foregoing in mind it is the principal objective of this invention to provide a system whereby the efficiency of a fossil fuel-fired steam generator is automatically and continuously monitored and is utilized by an automatic load control, such as described in U.S. Pat. No, 4,435,650, to control the distribution of the system load among a plurality of generators. This and further objectives of the invention will be apparent as the description proceeds in connection with the drawings in which: